1. Field of Invention
The present invention relates to a liquid crystal display and an electronic apparatus that incorporates the liquid crystal display, and more specifically, the invention relates to a transflective liquid crystal display.
2. Description of Related Art
Reflective liquid crystal displays have been employed as display units or the like in portable electronic apparatus. A problem occurs in that the display is difficult to see in a dark location, since the display relies on use of external light, such as natural light and artificial light. Thus, liquid crystal displays, which use external light in a bright place in the same way as general reflective liquid crystal displays, can still be used in a dark place by using a light of an illuminating device (hereinafter, referred to as a xe2x80x9cbacklightxe2x80x9d) on the reverse side of a liquid crystal cell. These displays are referred to as transflective liquid crystal displays.
A transflective liquid crystal display can be provided by, for example, converting a reflective liquid crystal display having an external reflector. This is accomplished by replacing a conventional reflector that has only a reflective function with a xe2x80x9ctransflective filmxe2x80x9d that has both a light transmissive function and a light reflective function. The transflective film can include a material with fine pearl pigments mixed therein, a metal film having an aperture for light transmission, or a metal film of very small thickness.
In addition, in recent years, as portable apparatus and OA (Office Automation) apparatus have been developed, there has been a growing demand for color liquid crystal displays. An even greater demand has been experienced for color liquid crystal displays and apparatus using reflective liquid crystal displays. However, when simply combining the transflective liquid crystal display of the above configuration with a color filter, the transflective film is disposed on the outer surface of the liquid crystal cell, and the color filter is disposed on the inner surface of the liquid crystal cell. Since a thick transparent substrate is interposed between the liquid crystal layer or the color filter and the transflective film, problems occur, such that a double reflection, a blur in the display, color mixing, etc. caused by parallax are generated, and a sufficient display quality cannot be obtained. Hereinafter, the surface on the liquid crystal layer side of each component of the liquid crystal layer is referred to as the xe2x80x9cinner surfacexe2x80x9d, and the surface on the side opposite to the liquid crystal layer is referred to as the xe2x80x9couter surfacexe2x80x9d.
In order to solve this problem, it has been proposed to provide a transflective liquid crystal display with a transflective film disposed on the inner surface side of the liquid crystal cell. FIG. 6 is a cross-sectional view showing one example of these liquid crystal displays. Two glass substrates 604, 612 provided with transparent electrodes 605, 609 are disposed on the inner surfaces facing each other, and a liquid crystal layer 607 is held between the glass substrates 604, 612 via alignment layers 606, 608 to form the liquid crystal cell. A transflective film 611, the color filter 610, the transparent electrode 609 and the alignment layer 608 are successively provided on the inner surface side of the lower glass substrate 612. In this configuration, the liquid crystal layer 607, the color filter 610 and the transflective film 611 are close to each other. The above problems, including the double reflection, the blur and the color mixture, can be solved with this structure.
Further, two retardation films 602, 603 and a polarizer 601 are successively provided on the outer surface side of the upper glass substrate 604.
Various parts to realize the transmissive display are disposed on the outer surface side of the lower glass substrate 612. For example, a xc2xc wavelength film 613 and a polarizer 614 are disposed on the outer surface of the lower glass substrate 612, and a backlight is disposed outside thereof. The backlight has a light source 617, a light guide plate 615 and a reflector 616. In the case of the reflective display, one polarizer 601 on the upper side has the functions of both a polarizer and an analyzer. On the other hand, in the case of the transmissive display, the polarizer 614 on the lower side functions as the polarizer, and the polarizer 601 on the upper side functions as the analyzer.
The reason for using the xc2xc wavelength film 613 is described below. Firstly, in the case of the reflective display, the light incident from the upper surface side of the liquid crystal cell, and transmitted through the liquid crystal layer, is preferably formed into a circularly polarized wave, or an elliptically polarized wave with high ellipticity, in a dark display condition, and formed into a plane-polarized wave, or an elliptically polarized wave with low ellipticity, in a bright display condition when it is reflected by the transflective film. This is because the circularly polarized wave, or the elliptically polarized wave with high ellipticity, reflected by the transflective film in the dark display condition, is formed into the plane-polarized wave, or the elliptically polarized wave with low ellipticity, orthogonal to the axis of transmission of the polarizer on the upper surface side of the liquid crystal cell through the re-transmission in the liquid crystal layer. This wave is absorbed in the polarizer. The dark display becomes darker, and an excellent contrast characteristic can be realized.
On the other hand, to realize a transmissive mode display similar to that of a reflective mode display, it is necessary that the light from the backlight is in the same polarized state as that in the reflective display when the light is transmitted through the transflective film. Specifically, the light is a circularly polarized wave or an elliptically polarized wave with high ellipticity. Thus, the xc2xc wavelength film is disposed between the polarizer and the transflective film to convert the plane-polarized wave after being transmitted through the polarizer into a circularly polarized wave, or an elliptically polarized wave with high ellipticity, when the light is transmitted through the transflective film after being emitted from the backlight.
In the above transflective liquid crystal display, in order to ensure the brightness of the reflective mode display making use of the reflected external light, the area of the aperture is set to be at most 10-25% of the whole area thereof in the case where a transflective film, having an aperture for light transmission, is provided therein, and the external light is reflected by the remaining area. Thus, in the transmissive mode, only a small portion of the light emitted from the backlight, and reaching the transflective film, is transmitted through the transflective film, and the remaining light is reflected by the outer surface side of the transflective film forming a limit to brighten the transmissive display.
On the other hand, there is a demand for a transflective liquid crystal display that brightens even in a transmissive mode, while maintaining the brightness in the reflective mode. However, it is difficult in principle to obtain brightness of both the reflective display and the transmissive display with only a transflective film configuration. In order to brighten the transmissive display while ensuring the brightness of the reflective display to some degree, it is necessary to increase the brightness of the backlight light source. However, to increase the brightness of the light source, the power consumption of the whole liquid crystal display is increased, and in particular, when the liquid crystal display is applied to portable electronic apparatus, etc., a problem occurs in that the battery life is shortened.
Accordingly, the present invention addresses the above problems, and an object of the present invention is to provide a transflective color liquid crystal display that enables a bright transmissive display and reduces the power consumption, without sacrificing the brightness of the reflective display.
In order to achieve the above object, a liquid crystal display of the present invention is provided that includes a liquid crystal layer that is held between a pair of substrates. A reflective display unit and a transmissive display unit are formed in one pixel. A retardation layer is formed in the transmissive display unit.
In the present invention, the light reflected by a transflective film to the backlight side is the same in the oscillating direction as that of the incident light, and is transmitted therethrough without being absorbed by a polarizer on the lower side of the liquid crystal display. This light is reflected again to the liquid crystal cell side by a reflector of the backlight, and re-used. As a result, the brightness of the transmissive display can be enhanced while maintaining the brightness of the reflective display compared with that of a conventional structure. Alternatively, the power consumption can be reduced, since the brightness of a light source can be reduced if the brightness of the transmissive display is on a certain level.
The retardation layer preferably has retardation of roughly xc2xc wavelength. Generally, a xc2xc wavelength film means that the retardation layer has a retardation of 140 nm. This retardation is xc2xc the wavelength of green light, and the retardation is 100 nm for blue light (a wavelength of 400 nm), and 150 nm for red light (a wavelength of 600 nm), and further, 180 nm for longer wavelength light (a wavelength of 720 nm). Thus, the range provided by the xc2xc wavelength film is not less than 100 nm to not more than 180 nm. Uniform retardation of the xc2xc wavelength can be easily realized if the retardation layer is formed of a polymer liquid crystal.
An electronic apparatus in accordance with the present invention includes the liquid crystal display described above. In the present invention, an electronic apparatus is realized that has display units that are bright in both the reflective display and the transmissive display and low in power consumption.